管道焊缝裂纹扩展的流固磁耦合表征

本工作利用虚拟裂纹闭合技术(Virtual crack closure technique,VCCT)提出一种单裂纹和多裂纹扩展通用的流固磁耦合方法,研究了流体压力的动态施加、流体-管道焊缝结构-磁场耦合作用下管道焊缝裂纹的扩展问题。该流固磁耦合方法每递增一次流体压力载荷,则完成一次裂纹增量扩展,更新裂纹几何形状,并重构网格,循环进行裂纹扩展计算和磁场分析,实现铁磁性管道焊缝裂纹扩展的流固磁耦合。以管道焊缝不同环向位置分布的单裂纹、多裂纹等六种工况为数值模拟算例,根据扩展结果中描述裂纹扩展的裂纹张开距离、裂纹扩展长度、磁感应强度水平分量峰值、磁感应强度垂直分量峰值等特征值,衡量裂纹所在位置的危险等级,判断管道焊缝损伤部位与损伤程度,识别多裂纹与单裂纹。该方法的实现可为在役管道焊缝裂纹的漏磁检测与评价、管道再制造修复等提供理论基础。

Characterization on Fluid-Solid-Magnetic Multifield Coupling of the Weld Cracks Growth in Pipelines

A general fluid-solid-magnetic coupling method for single-crack and multi-cracks growth was provided by using virtual crack closure technique (VCCT) in this paper. The growth behavior of cracks in the pipe lines, which affected by the action of the fluid-pipe weld structure-magnetic coupling effect with the dynamic increase of the fluid pressure, was investigated in detail. Results indicate that when the pressure load of the relevant fluid increases every time, this method completes a crack increment growth, and it renews the crack geometry, then the mesh is reconstructed and the crack growth calculation and magnetic field analysis are carried out in this cycle, and the fluid-solid-magnetic coupling of weld crack growth in ferromagnetic pipeline is achieved. The numerical simulation examples of single-crack and multiple-cracks in different circumferential position of pipe weld are taken as numerical examples. The crack opening distance and crack growth length of crack growth are described according to the growth results. The peak value of horizontal component of magnetic induction intensity and the peak value of vertical component of magnetic induction intensity are applied to measure the dangerous grade of the location of cracks, so as to judge the damage position and damage degree of pipeline weld, and it is also used to identify multiple cracks or single cracks. The realization of the method can provide a theoretical basis for the detection and evaluation of weld cracks in in-service pipeline by magnetic flux leakage method, and the remanufacture, repair of pipelines.